Fixed database service resource

Version 2.2+ of the puppetlabs-mysql moudule starts the MySQL database
with the Service resource name mysqld [1]. The puppet-heat module
lists a requirement for a Service resource with name mysql. This will
lead to an undefined resource error.

This patch corrects the dependency.

[1] https://github.com/puppetlabs/puppetlabs-mysql/blob/master/manifests/server/service.pp#L15

Change-Id: I2f60b610eab4d03552352108d0dfd4f2b796fc70